Device for coating aggregates, method and uses

ABSTRACT

The invention relates to a mixing device adapted to manufacture bituminous mixes comprising:at least one means for conveying at least one granulate, such as a recycled aggregate, towards a malaxator and/or a drying drum, said conveyor means having an upper face adapted to receive the granulate,several groups of infrared emitter(s), disposed in line with said upper face of said at least one conveyor means and which are adapted to emit a wavelength which substantially corresponds to the maximum wavelength in the determined absorption spectrum of said at least one granulate at a desired temperature, each group of infrared emitters being adapted to emit a specific wavelength which is different for each group, said at least one conveyor means being adapted to and/or configured so as to withstand the electromagnetic radiations emitted by said groups of infrared emitters.The invention also relates to the method for implementing the aforementioned device, as well as uses thereof.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of pavements intended for making wearing course, binder course, base course and/or road base course.

In particular, the present invention refers to a mixing device capable of recycling a substantial Reclaimed Asphalt Pavement (RAP) content, to a method for using the device, as well as uses thereof.

STATE OF THE ART

Under the influence of the ever more constraining road traffic and climatic attacks, the roads age, which, at the end of their lifetime, result in layers that no longer have the characteristics that comply with the required functions.

Recycling these old pavements has become a necessity with regards to environment protection: savings of natural resources (granulates), natural spaces (landfills), energy, reduction of greenhouse-effect gases.

All road materials are recyclable. They can be reused, either at the mixing plant or in place (on site), Recycling on site provides additional savings on transportation.

The recycled or recovered granulates comprise “Reclaimed Asphalt Pavement” (RAP).

By “RAP”, it means a granular mixture coming from milling, crushing, the demolition of patches, of surpluses or wastes of productions of old bituminous mixes (old pavement), and included in the composition of recycled coating (NF P 98-149 of June 2000).

By “recycled granulates” or “recyclates”, it means a set of grains with dimensions comprised between 0 and 125 mm originating from the demolition of constructions or being reused (NF EN 13-043 of August 2013).

RAPs may be classified into “specific aggregates” which are derived from a large amount of pavements to be recycled, generally well identified and homogenous (the same origin, archives, core-samplings) and “pit-run aggregates” which are essentially derived from small worksites, various demolitions or worksite returns. In general, the last type of RAP is crumbled in a crusher or a pelletiser, before being sieved to a maximum dimension ranging from 10 to 20 mm, exceptionally 25 mm for recycling in base courses. In general, RAPs are controlled and characterised in order to establish a Reclaimed Asphalt Pavement Technical Sheet (RAPTS) wherein various information are supplied: the residual binder content, the penetrability of the residual binder, the grain-size distribution analysis of the pavement granulates, as well as the intrinsic characteristics of the granulates (Los Angeles LA test, accelerated polishing coefficient (APC) test, etc.).

The degree of penetration of recycling operation varies a lot from one country to another, and even from one region to another. Thus, in Northern Europe, recycling is almost systematic. In the United-States, the situation is quite different from one State to another. Recycling has been expanding earlier and faster in highly urbanized areas in all countries, which are confronted with the growing distance from quarries and with the scarcity of landfill sites.

In France, the law of Jul. 13, 1992 prohibits in particular landfilling materials other than “ultimate” (non-reusable) wastes and imposes recycling of the materials included roadways. At the end of their service life, the materials included in roadways shall be used with a minimum supply of “fresh” materials.

Thus, various recycling techniques and devices, the selection of which depends on the nature of the material to be reused, its treatment mode, and the final destination of the resulting product, have been developed.

Indeed, the introduction percentage of RAPs in coating formulas, namely the recycling rate, is very dependent on the production tools, that is to say on the coating station.

Coating stations may allow for a discontinuous-station recycling (1), or a continuous-station recycling (2).

As regards discontinuous-station recycling (1), the coating stations (also called coating plants) generally include several pre-dosers, a drying drum, an elevator, and a malaxator with two bladed, horizontal and counter-rotating shafts. Recycling implies heating the recyclates (“aggregates”) without burning their bitumen and dosing them accurately in the final mixture.

Various introduction methods are in use:

Introduction from a Pre-Doser

The recyclates (minimum 5%) are sent towards the drying drum with the fresh granulates. This method is barely used at all, because while the granulates are recovered, the old bitumen is incinerated and is therefore lost.

Introduction onto the Elevator

The recyclates are added to the fresh granulates overheated beforehand in the drying drum. Drying and heating of the recycled pavements are performed by conduction in the elevator and it is necessary to lengthen the manufacture cycle. This method is simple and requires little investments. Nonetheless, overheating the fresh granulates (up to more than 200° C.) is very energy-intensive. In addition, this overheating could superficially alter some types of granulates, producing a non-negligible amount of ultrafines. Moreover, its efficiency becomes rapidly limited by the humidity of the recyclates and by vaporisation in the hot elevator. The maximum recycling rate is 10% with dry recyclates. In general, it could not exceed 5% if these are moist.

Introduction into the Drying Drum

The recyclates may also be added in the drying drum via a launcher mat installed in line with/in line with the drying drum, or via a recycling ring mounted on the drying drum. The maximum recycling time obtained according to this technique depends on the type of installation. It may be 10% (very humid recyclates) to 25% (dry recyclates) for a standard drier combined with a launcher mat, 15% (very humid recyclates) to 25% (dry recyclates) for an elongate drier combined with a launcher mat, or 20% (very humid recyclates) to 35% (dry recyclates) for an elongate drier combined with a recycling ring

Introduction into the Malaxator

The recyclates are introduced through a weighing hopper which opens directly into the malaxator. This method allows for a recycling rate up to 10% with very humid recyclates, 20% with dry recyclates. Sometimes, it is combined with an introduction of recyclates into the drying drum, in which case the overall recycling rate could reach 30 to 50%, depending on the humidity of the recyclates.

Introduction into Two Drying Drums Equipping the Recycling Station/Plant

Some stationary plants are equipped with two drying drums. The recyclates are dried and pre-heated to 120° C. in a parallel drum operating like a co-current drying-and-mixing drum (DMD). They are stored in a heat-insulated silo, and then dosed and sent into the malaxator. In parallel, the virgin granulates are overheated in the counter-current drying drum. After dosing, they are sent into the malaxator and homogenised with the recyclates and the filler blend. In this type of installations, the maximum recycling rate is from 35 to 40%, when the recyclates are very humid. It reaches 60% with dry recyclates. However, this technique has the drawback of being energy-intensive and quite expensive.

As regards continuous-station recycling (2), the coating stations are mostly equipped with DMD(s) which operate(s) in co-current flow or in counter-current flow.

Co-Current Recycling in DMD

The recyclates are introduced into the central portion of the drum via a recycling ring. First, the recyclates are continuously dosed, and then dried and heated up by the hot gases originating from the burner present in the DMD and by the virgin granulates overheated in the first portion of the tube. The recyclates are protected from the flame of the burner by the screen formed by the virgin granulated tanks to the arrangements of the troughs located inside the tube-like shaped DMD. Virgin granulates and recyclates are then homogenised in both grain-size distribution and temperature. Afterwards, the mixture passes into the kneading area, where the bitumen and the filler blend are injected. The maximum recycling rate depends on the humidity of the constituents and on the targeted temperature level for the end product; in general, it is from 20 to 30%.

Indeed, this limit cannot be exceeded because of the risk of clogging inside the DMD.

Counter-Current Recycling in DMD

The recyclates are introduced via a recycling ring positioned further than the middle of the tube. They are automatically protected from the flame of the burner. Afterwards, they are mixed with the virgin granulates overheated beforehand in the upstream portion of the drum. The bitumen and the filler blend arrive a short way downstream. The whole then passes into the kneading area. The maximum recycling rate ranges from 30 to 50% depending on the humidity in the recyclates and the temperature of the final mixture.

The “double-drum” station is a variant of the counter-current DMD that is widespread, inter alia, in the United-States under the name “Double Barrel”. The downstream portion is constituted by a concentric fixed cylinder into which arrive the overheated virgin granulates and are introduced the recyclates, the bitumen, and the filler blend. The rotating portion is provided with arms with blades, which perform a vigorous kneading.

Herein again, the maximum recycling rate is limited by the risk of clogging inside the DMD related to the presence of recyclates such as RAPs.

The following documents of the state of the art are also known.

The document EP 0 146 939 describes a device for manufacturing a new asphalt comprising a device for heating a used asphalt crushed beforehand. In particular, this heating device includes infrared radiators.

The document WO 2018/165768 describes an apparatus for heating up a bituminous mix, as well as an implementation method thereof. In particular, the bituminous mix heating apparatus may be used to repair an existing bituminous pavement coating or for the building of a new pavement coating. In particular, the heating apparatus comprises an infrared emitter, a burner tube coupled to the infrared emitter and a Venturi tube.

The document CN 101 187 196 describes a device for heating up a pavement aggregate in order to recycle it. In particular, the heating device comprises an infrared emitter. Thus, there is a need to provide new coating/recycling devices allowing manufacturing bituminous mixes comprising a relatively high content of recyclates, such as RAPs.

There is also a need to provide a new coating/recycling device that avoids at least the risks of clogging within the drying drums, while being simple to implement and which could be adapted to the different existing coating/recycling stations such as those mentioned hereinabove (continuous station, discontinuous station).

Thus, the present invention aims to provide a new coating/recycling device that avoids, at least in part, the aforementioned drawbacks.

The present invention provides a technical solution to the problems identified hereinabove.

DISCLOSURE OF THE INVENTION

The present invention provides a mixing device adapted to manufacture bituminous mixes comprising:

at least one means for conveying at least one granulate, such as a recycled aggregate, towards a malaxator and/or a drying drum, said conveyor means having an upper face adapted to receive the granulate,

several groups of infrared emitter(s), disposed in line with said upper face of said at least one conveyor means and which are adapted to emit a wavelength which substantially corresponds to the maximum wavelength in the determined absorption spectrum of said at least one granulate at a desired temperature, each group of infrared emitters being adapted to emit a specific wavelength which is different for each group, said at least one conveyor means being adapted to and/or configured so as to withstand the electromagnetic radiations emitted by said groups of infrared emitters.

The Applicant has surprisingly discovered that it was possible to heat up one or several type(s) of granulates, and in particular RAPs via at least one infrared emitter and in particular two groups of infrared emitter(s) sized with regards to the characteristics of the aggregate(s) to be heated up. Thus, the granulate(s) is/are heated up beforehand to a temperature that could reach 250° C. in a few seconds (90 s) before being conveyed towards the malaxator or the drying drum thereby avoiding any risk of clogging, in particular when the granulate is a RAP.

Furthermore, according to the invention, the mixing device comprises several groups of infrared emitter(s), such as at least two groups of infrared emitter(s) each being adapted to emit a specific wavelength which is dedicated to a specific granulate. Thus, the emitted wavelengths are generally different.

Other non-limiting and advantageous features of the mixing device in accordance with the invention, considered separately or according to any technically feasible combinations, are as follows:

-   -   the wavelength of said at least one emitter (namely the infrared         emitter(s) of the groups of infrared emitter(s) according to the         invention) ranges from 0.7 micrometer to 1 mm, preferably from 1         to 80 micrometer(s) and typically from 1 to 50 micrometer(s);     -   the device comprises at least one enclosure disposed so as to         form a tunnel with at least one portion of said at least one         conveyor means, preferably the entirety of said at least one         conveyor means and which has an internal face on which said at         least one emitter, namely all or part of said groups of infrared         emitter(s), are arranged;     -   1 to 20 panel(s) of infrared emitter(s) each comprising from 1         to 50 infrared emitter(s), preferably from 2 to 40 infrared         emitters and typically from 4 to 24 infrared emitters, is/are         arranged on said internal face of said at least one enclosure;     -   said at least one emitter (namely the infrared emitter(s) of the         groups of infrared emitter(s) according to the invention) is a         carbon infrared emitter;     -   the groups of infrared emitter(s) are in the form of panels of         infrared emitter(s), preferably each group of infrared         emitter(s) is in the form of one or several panel(s) of infrared         emitter(s);     -   the distance “d” between the internal face of said at least one         enclosure where the emitter(s) or the panel(s) of infrared         emitter(s) is positioned and said upper face of said conveyor         means ranges from 10 to 250 mm, preferably from 15 to 200 mm and         typically from to 200 mm and in particular from 35 to 100 mm;     -   the tunnel extends on a longitudinal axis, denoted X, and         measures from 8.0 m to 12.5 m (depending on the production         parameters);     -   the tunnel extends according to a longitudinal axis X, the         lateral spacing denoted “y” between two panels of emitter(s),         considered in a sectional plane transverse to the longitudinal         axis X, ranges from 600 mm to 1200 mm, preferably from 600 mm to         800 mm and is typically 600 mm (depending on the production         parameters);     -   the longitudinal spacing denoted “z” between two panels of         emitter(s), considered in the longitudinal plane X, ranges from         0 to 100 mm, preferably from 50 mm to 100 mm and is typically         100 mm;     -   the device comprises at least:

a conveyor means for each type of granulates, such as a conveyor means for virgin granulates (chippings, sands) and a conveyor means for recycled granulates (pavement aggregates); and/or

a conveyor means for different types of granulates, such as a conveyor means for both virgin granulates and recycled granulates; the conveyor means is therefore unique;

-   -   all conveyor means are adapted to and/or configured so as to         withstand the electromagnetic radiations emitted by the infrared         emitter(s);     -   the conveyor means is/are made of steel;     -   the device comprises several groups of emitters or several         groups of panels of emitters, each group being adapted to emit a         specific wavelength which is different for each group (in         particular, the specific wavelength of each group of emitters or         each group of panels of emitters substantially corresponds to         the maximum wavelength in the absorption spectrum of a type of         granulates to which the emitters or panels of emitters are         associated at a desired temperature);     -   the groups of emitters or of panels of emitters are distributed         over different portions of the enclosure, as in the case where         the device is provided with a conveyor means for different types         of granulates, or the groups of emitters or of panels of         emitters are distributed over different conveyor means, as in         the case where the device is provided with a different conveyor         means for each type of granulates.

Thus, the device comprises:

-   -   one single enclosure, each group of infrared emitter(s) being         distributed over different portions of said enclosure, so that         the device is provided with the same conveyor means for         different types of granulates;     -   different enclosures, each enclosure being specific to one         conveyor means, which, in turn, is dedicated to one type of         granulates and each group of infrared emitter(s) being         distributed over a different enclosure, so that said device is         provided with different conveyor means for different types of         granulates.

The present invention also refers to a method for implementing the mixing device as described hereinabove, comprising the following steps:

(a) determining, at a desired temperature, the maximum wavelength in the absorption spectrum determined by spectrography of several types of granulates to be heated up which are generally different, such as a first recycled aggregate, a second recycled aggregate (from an origin different from the first one), a virgin granulate such as sands, chippings;

(b) disposing on said mixing device several groups of infrared emitter(s), each group of infrared emitter(s) being adapted to or being configured so as to emit substantially the wavelength determined at step (a) for a given type of granulates;

(c) successively conveying via said conveyor means each type of granulates in line with said group of infrared emitter(s) that corresponds thereto and apply the wavelength so as to heat it up by thermal radiation;

(d) conveying each type of heated granulates from step (d) towards the malaxator and/or the drying drum comprising at least one hydrocarbon binder and optionally at least one virgin granulate (fines, sands, chippings), so as to manufacture a bituminous mix.

Preferably, steps (a) to (c) are thus carried out for different types of granulates that might have a different maximum wavelength, such as virgin granulates (fines, sands, chippings) or recycled granulates (pavement aggregates).

The present invention also provides for the use of the device as described hereinabove to recycle non-virgin aggregates, or to manufacture of a bituminous mix.

DETAILED DESCRIPTION OF THE INVENTION

The following description with reference to the appended drawings, provided as non-limiting examples, will better explain the object of the invention and how it could be carried out.

In the appended drawings:

FIG. 1 is a side view schematically representing a mixing device having a longitudinal axis X-X according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view with respect to the longitudinal axis X-X of the mixing device of FIG. 1, and

FIG. 3 is a top view of a cross-section of the mixing device of FIG. 1 according to the axis Y-Y.

It should be noted that in these figures, structural and/or functional elements that are common to the different variants may bear the same reference numerals.

Referring to FIGS. 1 to 3, a mixing device according to an embodiment of the invention will be described. According to the embodiment described hereinafter and which does not limit the invention, different groups of infrared emitter(s) that are adapted to emit a specific wavelength that is different for each group are disposed on one single conveyor means. Alternatively, it is possible to provide for each group of infrared emitter(s) to be disposed on a different conveyor means, namely the device includes several conveyor means each being dedicated to convey one type of granulates and each including a specific group of infrared emitter(s).

As mentioned hereinabove, a mixing device according to the invention is adapted to manufacture bituminous mixes. By “bituminous mixes”, it means a granulate covered with bitumen, used in roadway pavements. In particular, the mixing device 100 is adapted to manufacture recycled coatings (NF P 98-149 of June 2010). As defined herein, a “recycled coating” means a hot- or cold-hydrocarbonated coating including, in its entirety or in part thereof, recycled materials (pavement aggregates derived from either milling-mill or demolition of existing pavements), whether the manufacture occurs in plant or on site.

For this purpose, the mixing device 100 comprises at least: a conveyor means 1 of at least one granulate 5 which is generally a scraper conveyor 1, a malaxator and/or a drying drum 3 and an enclosure for storing the granulate 5.

For the following description, the term “scraper conveyor” will be used as represented in the figures.

In particular, this scraper conveyor 1 is connected at one of its ends to the enclosure for storing the granulate 5, such as a pre-doser 2 and at its other end to the malaxator or a drying drum 3. Alternatively, the scraper conveyor 1 may be connected to one or several granulate storage enclosure(s), namely to several pre-dosers, each pre-doser being specific to a given granulate (RAP, sands, chippings, etc.).

According to the invention, by “granulate”, it means a set of grains with dimensions comprised between 0 and 25 mm included in particular in the composition of a roadway. The term granulate encompasses different types of materials, such as fines, sands, chippings, gravels or RAP.

The storage enclosure or pre-doser 2 that is suitable for the present invention is known to those skilled in the art and will not be described in more detail hereinafter. It may consist of a dosing hopper enabling the storage, and the volumetric or weight dosing of a granulate.

Similarly, the malaxator and the drying drum 3 are known to those skilled in the art and will not be described in more detail hereinafter. These means are respectively intended to knead/dry the different compounds included in the formulation of the bituminous mix. In the case of a DMD, kneading and drying are performed in the same apparatus.

In particular, the scraper conveyor 1 according to the invention with the axis X-X is disposed horizontally (with respect to the ground) as represented in FIG. 1. Alternatively, the scraper conveyor 1 may be inclined, the bottom portion being generally disposed on the side of the pre-doser 2 and the top portion being disposed on the side of the drying drum 3.

In general, the scraper conveyor 1 has in particular an upper face 4 adapted to receive the granulate(s) 5. As represented herein, the granulate 5 may at first consist preferably of a RAP and secondly of another granulate, such as sands and/or chippings. As explained hereinabove, recycling of RAPs is currently limited in particular because of clogging problems within the drying drums. The device 100 according to the invention allows overcoming this problem.

To this end, the mixing device 100 includes opposite the upper face 4 of the scraper conveyor 1, at least several groups of infrared emitter(s), namely at least two which are adapted to emit a wavelength that substantially corresponds to the maximum wavelength in the absorption spectrum determined by absorption spectrography of said at least one granulate at a desired temperature. In particular, each group of infrared emitters is adapted to emit a specific wavelength which is different for each group and which is therefore dedicated to one type of granulates (that is to say for example a first RAP, or a second RAP different from the first one, or sands or chippings, etc.).

In general, the absorption spectrum of the granulate(s) is determined spectroscopy. Since each granular material emits a wavelength specific to its molecular composition which directly depends on its temperature, it is possible to have a feedback on the wavelength emitted by the granular material at a desired temperature (Planck's law) using a spectral camera or an infrared camera.

Indeed, the differences in the atomic structure of the granulates to be heated up (in particular because of their water, bitumen content or sill of their nature: granite, limestone, etc.) imply that each of these granulates has its own spectral domain within which the absorption of the radiation is optimum. Indeed, each granulate has its own absorption rate. The radiation particles that are not absorbed by the granule cross it or undergo a reflection.

Furthermore, said conveyor means, herein the scraper conveyor 1, is adapted to and/or configured so as to withstand the electromagnetic radiations emitted by the infrared emitter(s).

Typically, the scraper conveyor 1 is made of steel.

Preferably, the mixing device 100 comprises an enclosure 6, disposed so as to form a tunnel with at least one portion of the scraper conveyor 1, preferably the entirety of the scraper conveyor 1. The enclosure 6 has an upper face 9 and an internal face 8 on which said groups of infrared emitter(s) are arranged.

Preferably, the groups of infrared emitter(s) are in the form of panels of infrared emitter(s), preferably each group of infrared emitter(s) is in the form of one or several panels of infrared emitter(s).

For example, 1 to 20 panels of infrared emitter(s) each comprising from 1 to 50 infrared emitter(s), preferably from 2 to 40 infrared emitter(s) and typically from 4 to 24 infrared emitter(s) is/are arranged on said internal face 8 of the enclosure 6. The enclosure 6 may also comprise venting orifices 7.

In general, the tunnel extends according to the longitudinal axis X and measures from 8.0 m to 12.5 m.

Preferably, in order to determine the maximum absorption of the granulate such as a pavement aggregate RAP, it is possible to proceed as follows: a sample of RAP aggregates (granulate) is heated up to the desired temperature (a representative sample of substantially 5.0 kg) in a conventional aggregate furnace. Once the sample has reached the desired temperature, a spectral camera is used in order to determine the length emitted by the RAP/recycled materials aggregates. Thus, the maximum wavelength in the absorption spectrum of the sample of RAP aggregates at a desired temperature is determined. Afterwards, this wavelength will be applied in order to heat up the aggregate. It is proceeded the same for the other type(s) of granulates (RAP of a different origin, sands, chippings, etc.).

In general, the wavelength of said at least one emitter, namely said at least one emitter constituting one of the groups of infrared emitter(s), ranges from 0.7 micrometer to 1 mm, preferably from 1 to 80 micrometer(s) and typically from 1 to 50 micrometer(s).

In particular, the temperature within the granulate 5, measured for example with one or several infrared thermometer(s) located at the outlet of the different scraper conveyor(s) 1 ranges from 20 to 200° C., preferably from 80 to 150° C. and typically from 110 to 150° C.

Thus, when the granulate 5 reaches the malaxator or the drying drum 3, it generally has an inlet temperature that is lower from 20 to 50° C., preferably from 30 to 40° C. with respect to the temperature inside the malaxator/drying drum 3.

Preferably, the infrared emitters consist of carbon infrared emitters.

According to this embodiment, a carbon infrared emitter that is suitable for the present invention may correspond to the infrared emitter commercialised by Heraeus under the trademark CIR®.

It may have the characteristics summarised in the following Table 1:

Emitters

TABLE 1 Double-tube carbon Round-tube carbon infrared emitters infrared emitters Power 60 W/cm 30 W/cm Max. heated length 5000 mm 1500 mm Section 34 × 14 mm 19 mm Temperature of 1200° C. 1200° C. the filament Wavelength 2 micrometers 2 micrometers Max. surface 110 kW/m² 85 kW/m² efficiency Response time 1-2 s 1-2 s

In particular and as mentioned hereinabove, the device 100 includes several groups of infrared emitter(s), each group comprising several infrared emitters.

According to a feature of the invention, the IR emitter(s) according to the invention are powered by electricity.

Also, depending on the nature, the humidity and the amount of granulate to be heated up, it is possible to act on several parameters, such as: the distance between the emitters or panels of emitters and/or the distance between the scraper conveyor 1 and the emitters/panels of emitters for each group of IR emitter(s) and/or the number of emitters evenly positioned along the scraper conveyor 1 for each group of IR emitters.

In particular, the distance “d” between the internal face of the enclosure where the emitter(s) or the panel(s) of emitters of a group of IR emitter(s) are positioned and the upper face of the scraper conveyor 1 ranges from 10 to 250 mm, preferably from 15 mm to 200 mm and typically from 20 mm to 200 mm and in particular from 35 mm to 100 mm.

According to the invention, a distance “d” ranging from 10 to 250 mm comprises the following values and any interval comprised between these values: 10; 20; 30; 40; 50; 60; 70; 80; 90; 100; 110; 120; 130; 140; 150; 160; 170; 180; 190; 200; 210; 220; 230; 240 and 250 mm.

Also, the lateral spacing denoted “y” between two panels of emitter(s) of the same group of IR emitters, considered in a sectional plane transverse to the longitudinal axis X, may range from 600 mm to 1200 mm, preferably from 600 mm to 800 mm and is typically 600 mm (depending on the production parameters).

According to the invention, a lateral spacing “y” ranging from 600 to 1200 mm comprises the following values and any interval comprised between these values: 600; 700; 800; 900; 1000; 1100 and 1200 mm.

Finally, the longitudinal spacing denoted “z” between two panels of emitter(s) of the same group of IR emitters, considered in the longitudinal plane X, ranges from 0 mm to 100 mm, preferably 50 mm to 100 mm and is typically 100 mm.

According to the invention, a longitudinal spacing “z” ranging from 0 to 100 mm comprises the following values and any interval comprised between these values: 0 (two adjacent panels in direct contact with one another); 20; 30; 40; 50; 60; 70; 80; 90 and 100 mm.

According to the embodiment illustrated in FIGS. 1 to 3, the device 100 according to the invention comprises a scraper conveyor 1 for different types of granulates, namely the device comprises one single scraper conveyor 1 for all of the granular mixture included in the formulation of the coating to be formed (one scraper conveyor 1 for virgin granulates and recycled granulates).

Thus, according to this embodiment, the device 100 comprises one single enclosure, each group of infrared emitter(s) being distributed over different portions of said enclosure, so that the device is provided with the same conveyor means for different types of granulates.

In particular, the enclosure 6 may comprise several groups of IR emitters, each group being set differently so as to heat up the different granulates according to their nature, their moisture content, etc. According to this embodiment represented in FIG. 3, along the scraper conveyor 1, it is possible to provide for different possible heating areas, for example ranging from 2 to 6, and in particular 4 different heating areas denoted in FIG. 3 heating areas A to D. Thus, FIG. 3 shows 4 groups of IR emitters according to the invention.

Thus, according to this embodiment, the different groupings of emitters of the areas A to D may be set on intervals with different wavelengths so as to enable heating different types of granulates (fines, crushed stones, chippings, gravels, etc. or RAPs having a different composition from one another). Similarly, the determination of the adequate wavelength substantially corresponds to the maximum wavelength n the determined absorption spectrum of the granulate associated to the different groups of emitters of the areas A to D and that being so at a desired temperature.

For example, the different groups of IR emitters may allow heating up pavement aggregates of different origins and the non-recycled or virgin granulates, such as sands and chippings, may be conveyed towards the drying drum/malaxator via another conveyor means or via the scraper conveyor 1 but without necessarily being heated up by a group of IR emitter(s).

According to another embodiment, the device 100 according to the invention may comprise a conveyor means as described hereinabove (namely surmounted by an enclosure comprising one or several emitter(s)) for each type of granulates, such as a scraper conveyor 1 for virgin granulates, such as chippings, sands and another scraper conveyor 1 for recycled granulates (pavement aggregates), each of the scraper conveyors being provided with a group of IR emitters which is specific thereto or which is sized so as to heat up the granulate that has to be transported in said conveyor.

Thus, according to this other embodiment, the device 100 includes different enclosures, each enclosure being specific to one conveyor means, which, in turn, is dedicated to one type of granulates and each group of infrared emitter(s) being distributed over a different enclosure, so that said device is provided with different conveyor means for different types of granulates.

The Applicant has estimated that the mixing device according to the invention could allow heating up 25 to 50 tons of RAP. In general, for a 50 mm thickness of RAP, the reached temperatures amount to 101° C. in 60 seconds and 243° C. in 90 seconds. It has also been estimated that the energy demand amounts to about 125 000 kJ per metric ton compared to 250 000 kJ per metric ton with the current methods described hereinabove.

Consequently, the mixing device 100 according to the invention has many advantages in comparison with the conventional methods that are currently in use.

Indeed, first of all, it allows avoiding clogging of the drying drums which is one of the reasons of limited use of RAPs. To the extent that RAPs are not heated up in the drying drums, but upstreams on the scraper conveyor 1, the RAPs reach the drying drum already at a temperature of 100-120° C. and therefore there is no thermal shock with the virgin granulates already present in the drying drum, in general at a temperature ranging from 150° C. to 170° C. At the outlet of the drying drum, the granular mixture (including the virgin granulates (fines, sands, chippings originating from a quarry) and RAPs) mixed with fresh bitumen has a temperature of about 120-150° C.

Then, the device according to the invention does not induce any modifications of the granulate to be heated up, even when this consists of a RAP.

Also, the device 100 requires a relatively low investment and may fit to all current devices, such as those described hereinabove in the prior art.

Furthermore, to the extent that it allows for an energy demand saving, not only it allows achieving a financial saving, but also reducing the environmental cost.

The present invention also covers a method for implementing the mixing device as described hereinabove, comprising the following steps:

determining, at a desired temperature, the maximum wavelength in the absorption spectrum determined by spectrography of at least one granulate to be heated up, such as a recycled aggregate;

disposing on said mixing device at least one infrared emitter adapted to or configured so as to emit substantially the wavelength determined at step (a);

conveying via said conveyor means said granulate in line with said at least one infrared emitter;

applying the wavelength on said granulate so as to heat it up by thermal radiation,

conveying said heated granulate from step (d) towards the malaxator and/or the drying drum comprising at least one hydrocarbon binder and at least one virgin granulate (fines, sands, chippings), so as to manufacture a bituminous mix.

Of course, the features described hereinabove for the mixing device are replicated herein in their entirety to characterise the method according to the invention.

In general, steps (a) to (c) below are carried out for different types of granulates that might have a different maximum wavelength, such as virgin granulates (fines, sands, chippings) or recycled granulates (pavement aggregates).

In particular, the method according to the invention comprises the following steps:

(a) determining, at a desired temperature, the maximum wavelength in the absorption spectrum determined by spectrography of several types of granulates to be heated up which are different, such as a recycled aggregate, a virgin granulate such as sands, chippings;

(b) disposing on said mixing device several groups of infrared emitter(s), each group of infrared emitter(s) being adapted to or being configured so as to emit substantially the wavelength determined at step (a) for a given type of granulates;

(c) successively conveying via said conveyor means each type of granulates in line with said group of infrared emitter(s) that corresponds thereto and apply the wavelength so as to heat it up by thermal radiation;

(d) conveying each type of heated granulates from step (d) towards the malaxator and/or the drying drum comprising at least one hydrocarbon binder and optionally at least one virgin granulate (fines, sands, chippings), so as to manufacture a bituminous mix.

The present invention also refers to the use of the mixing device as described hereinabove to recycle non-virgin aggregates or to manufacture a bituminous mix.

Of course, the features described hereinabove for the mixing device are replicated herein in their entirety to characterise the uses of the mixing device according to the invention.

Examples A°) RAW MATERIALS RAP

!TABLE 2 RAP RAP Characteristics Before drying After drying Humidity % 5.60 <1% % A/C* 3.66 3.66 Origin Witecourt 10 mm Whitecourt 10 mm *The “% A/C” ratio corresponds to the ratio between the mass of the granular mixture (RAP) and the bitumen mass contained inside this same granular mixture. In this instance, the used sample has a bitumen mass equal to 3.66% of the total mass of the sample. Grain-size distribution of the tested RAPs

TABLE 3 μm 12 500 10 000 5 000 2 500 1 250 630 315 160 80 % mass 100% 95% 75% 61% 52% 45% 30% 18% 11.80%

Emitters (600 mm by 600 mm Panels)

TABLE 4 Characteristics Carbon-type emitters Name of the product 600 mm long twin tube Number 12 d* Variable (125 mm; 25 mm; 150 mm) y* 600 mm z* 35 mm Thickness of the RAPs 50 mm Total energy 8525 W Voltage 460 V Current 18.75 Amps frequency 60 Hz *as defined hereinabove in the description

B°) PROTOCOL FOR HEATING UP A TYPE OF GRANULATES (RAP)

Drying Procedure

About 5 Kg of RAPs as defined in paragraph A° have been in a 600 mm by 600 mm sized metallic container;

The exact mass of the RAPs has been reported;

The RAPs have been placed beneath the emitters as defined in Table 4 at different distances “d”: 25 mm, 125 mm and 150 mm;

The mass and the temperature of the exposed RAP have been measured every 30 seconds for 3 minutes. The temperature of each emitter has been recorded every 30 seconds for the same time period.

Heating Procedure

About 5 Kg of RAPs (humidity <1 weight % with respect to the total mass of the RAP) as defined in paragraph A° have been in a 600 mm by 600 mm sized metallic container;

The exact mass of the RAPs has been reported;

The RAPs have been placed beneath the emitters as defined in Table 4 at different distances “d”: 25 mm, 125 mm and 150 mm;

The mass and the temperature of the exposed RAP have been measured every 60 seconds for 3 minutes. The temperature of each emitter has been recorded every 60 seconds for the same time period.)

C°) RESULT

Drying Procedure

D=125 mm

TABLE 5 t 0 t 60 t 120 t 180 Mass of the sample (g): 7743.6 7559.1 7438.3 7401.1 Humidity % 5.6 3.3 1.7 1.2 T sample (C°): 18.3 192.5 228.9 264.2 T° emitter (C°): 1159.0 1159.0 1159.0 1159.0 Consumed energy (kJ): 0.0 517.5 1035.0 1552.5 Energy (kJ)/Mass t 0 (kg): 0.0 66.8 133.7 200.5

D=180 mm

TABLE 6 t 0 t 60 t 120 t 180 Mass of the sample (g): 7977.2 7880.3 7772.0 7651.1 Humidity % 5.6 4.4 3.1 1.6 T sample (C°): 18.3 176.4 206.6 263.7 T° emitter (C°): 1159.0 1159.0 1159.0 1159.0 Consumed energy (kJ): 0.0 517.5 1035.0 1552.5 Energy (kJ)/Mass t 0 (kg): 0.0 64.9 129.7 194.6

Heating Procedure

D=25 mm

TABLE 7 t 0 t 60 t 120 t 180 Mass of the sample (g): 5140.0 5105.0 5092.0 5080.0 Humidity % 0.8 0.1 −0.2 −0.4 T sample (C°): 18.2 135.2 189.9 251.1 T° emitter (C°): 475.0 476.6 478.0 480.0 Consumed energy (kJ): 0.0 463.7 927.4 1391.0 Energy (kJ)/Mass t 0 (kg): 0.0 90.2 180.4 270.6

D=150 mm)

TABLE 8 t 0 t 60 t 120 t 180 Mass of the sample (g): 5005.0 5000.0 4995.0 4985.0 Humidity % 0.8 0.7 0.6 0.4 T sample (C°): 15.0 100.1 169.3 192.8 T° emitter (C°): 1175.0 1175.0 1175.0 1175.0 Consumed energy (kJ): 0.0 517.5 1035.0 1552.5 Energy (kJ)/Mass t 0 (kg): 0.0 0103.4 206.8 310.2

D°) CONCLUSION

The carbon IR emitter allows heating up recycled aggregates, such as RAPs, in a very efficient manner.

Of course, it is possible to provide for another group of IR emitters in order to heat up another type of granulates (RAP of a different origin, sands or chippings). This example primarily aims to demonstrate that a first group of emitters that has been sized beforehand to heat up the RAP of Table 2 is effective. 

1-14. (canceled)
 15. A mixing device adapted to manufacture bituminous mixes comprising: at least one means for conveying at least one granulate having a determined absorption spectrum at a desired temperature towards a malaxator and/or a drying drum, said conveyor means having an upper face adapted to receive the granulate, several groups of infrared emitter(s), disposed in line with said upper face of said at least one conveyor means and which are adapted to emit a wavelength which substantially corresponds to a maximum wavelength in the determined absorption spectrum of said at least one granulate at the desired temperature, each group of infrared emitters being adapted to emit a specific wavelength which is different for each group, said at least one conveyor means being adapted to and/or configured so as to withstand the electromagnetic radiations emitted by said groups of infrared emitters.
 16. The mixing device according to claim 15, wherein the wavelength of said groups of infrared emitter(s) ranges from 0.7 μm to 1 mm.
 17. The mixing device according to claim 16, wherein the wavelength of said groups of infrared emitter(s) ranges from 1 to 80 μm.
 18. The mixing device according to claim 16, wherein the wavelength of said groups of infrared emitter(s) ranges from 1 to 50 μm.
 19. The mixing device according to claim 15, comprising at least one enclosure disposed so as to form a tunnel with at least one portion of said at least one conveyor means and which has an internal face on which all or part of said groups of infrared emitter(s) are arranged.
 20. The mixing device according to claim 19, which comprises: a conveyor means for each type of granulates; or a conveyor means for different types of granulates.
 21. The mixing device according to claim 20, wherein said mixing device comprises: one single enclosure, each group of infrared emitter(s) being distributed over different portions of said enclosure, so that the device is provided with the same conveyor means for different types of granulates; different enclosures, each enclosure being specific to one conveyor means, which, in turn, is dedicated to one type of granulates and each group of infrared emitter(s) being distributed over a different enclosure, so that said device is provided with different conveyor means for different types of granulates.
 22. The mixing device according to claim 15, wherein the groups of infrared emitter(s) are in the form of panels of infrared emitter(s).
 23. The mixing device according to claim 22, wherein each group of infrared emitter(s) is in the form of one or several panel(s) of infrared emitter(s).
 24. The mixing device according to claim 22, wherein 1 to 20 panel(s) of infrared emitter(s) each comprising from 1 to 50 emitter(s), is/are arranged on said internal face of said at least one enclosure.
 25. The mixing device according to claim 15, wherein the infrared emitters consist of carbon infrared emitters.
 26. The mixing device according to claim 19, wherein the distance “d” between the internal face of said at least one enclosure where the panel(s) of infrared emitter(s) is positioned and said upper face of said conveyor means ranges from 10 mm to 250 mm.
 27. The mixing device according to claim 26, wherein the distance “d” ranges from to 200 mm.
 28. The mixing device according to claim 26, wherein the distance “d” ranges from nm to 100 nm.
 29. The mixing device according to claim 22, wherein the tunnel extends according to a longitudinal axis X, the lateral spacing denoted “y” between two panels of emitter(s), considered in a sectional plane transverse to the longitudinal axis X, ranges from 600 mm to 1200 mm.
 30. The mixing device according to claim 29, wherein the lateral spacing denoted “y” ranges from 600 mm to 800 mm.
 31. The mixing device according to claim 22, wherein the longitudinal spacing denoted “z” between two panels of emitter(s), considered in the longitudinal plane X, ranges from 0 to 100 mm.
 32. The mixing device according to claim 31, wherein the longitudinal spacing denoted “z” between two panels of emitter(s), considered in the longitudinal plane X, ranges from 50 mm to 100 mm.
 33. The mixing device according to claim 31, wherein the longitudinal spacing denoted “z” between two panels of emitter(s), considered in the longitudinal plane X is 100 mm.
 34. A method for implementing the mixing device according to claim 15, comprising the following steps: (a) determining, at a desired temperature, the maximum wavelength in the absorption spectrum determined by spectrography of several types of granulates to be heated up which are different; (b) disposing on said mixing device several groups of infrared emitter(s), each group of infrared emitter(s) being adapted to or being configured so as to emit substantially the wavelength determined at step (a) for a given type of granulates; (c) successively conveying via said conveyor means, each type of granulates in line with said group of infrared emitter(s) that corresponds thereto and applying the wavelength so as to heat the granulates by thermal radiation; (d) conveying each type of heated granulates from step (c) towards the malaxator and/or the drying drum including at least one hydrocarbon binder, so as to manufacture a bituminous mix.
 35. The method according to claim 34, wherein the several type of granulates are selected from recycled aggregate or virgin granulates.
 36. The method of claim 34, wherein the drying drum further includes at least one virgin granulate. 